Advancements in display technology, including the development of plasma display panels (PDPs) and plasma addressed liquid crystal (PALC) displays, have led to an interest in forming electrically-insulating ceramic barrier ribs on glass substrates. The ceramic barrier ribs separate cells in which an inert gas can be excited by an electric field applied between opposing electrodes. The gas discharge emits ultraviolet (uv) radiation within the cell. In the case of PDPs, the interior of the cell is coated with a phosphor which gives off red, green, or blue visible light when excited by uv radiation. The size of the cells determines the size of the picture elements (pixels) in the display. PDPs and PALC displays can be used, for example, as display screens in high definition television (HDTV) or other digital electronic displays.
Various methods have been used to fabricate ceramic barrier ribs for PDPs. One method is repeated screen printing. In this method, a screen is aligned on the substrate and used to print a thin layer of barrier rib material. The screen is removed and the material is hardened. Because the amount of material that can be printed with this technique is insufficient to create ribs having the desired height (typically about 100 μm to 200 μm), the screen is then realigned and a second layer of barrier rib material is printed on top of the first layer. The second layer is then hardened. Layers of rib material are repeatedly printed and hardened until the desired barrier height is achieved. The multiple alignment and hardening steps required with this method results in a long processing time and poor control of the overall barrier rib profile shape.
Another method involves masking and sandblasting. In this method, a substrate having electrodes is coated with the barrier rib material which is partially fired. A mask is then applied to the barrier material using conventional lithography techniques. The mask is applied on the areas between the electrodes. The substrate is then sandblasted to remove the barrier rib material exposed by the mask. Finally, the mask is removed and the barrier ribs are fired to completion. This method requires only one alignment step and can therefore be more accurate than the multiple screen printing method. However, because the area of the finished substrate covered by barrier ribs is small, most of the barrier rib material must be removed by sandblasting. This large amount of waste increases the production cost. In addition, because the barrier rib material often includes lead-based glass frit, environmentally-friendly disposal of the removed material is an issue. Also, while the positions of the ribs after sandblasting can be quite accurate, the overall shapes of the ribs, including the height-to-width aspect ratio, can be difficult to control.
Another process utilizes conventional photolithographic techniques to pattern the barrier rib material. In this technique, the barrier rib material includes a photosensitive resist. The barrier rib material is coated onto the substrate over the electrodes, often by laminating the rib material in the form of a tape onto the substrate. A mask is applied over the barrier rib material and the material is exposed by radiation. The mask is removed and the exposed areas of the material are developed. Barrier rib material can then be removed by washing to form the rib structures. This process can give high precision and accuracy. However, as with sandblasting, much material is wasted because the entire substrate is initially coated with the barrier rib material and the ribs are patterned by material removal. Another process involves using a mold to fabricate barrier ribs. This can be done by direct molding on the substrate or by molding on a transfer sheet and then transferring the ribs to a substrate. Direct molding onto a substrate involves coating either the substrate or the mold with barrier rib material, pressing the mold against the substrate, hardening the material on the substrate, and removing the mold. For example, Japanese Laid-Open Patent Application No. 9-134676 discloses using a metal or glass mold to shape barrier ribs from a glass or ceramic powder dispersed in a binder onto a glass substrate. Japanese Laid-Open Patent Application No. 9-147754 disclosed the same process where electrodes are transferred to the substrate simultaneously with the barrier ribs using a mold. After hardening the barrier rib material and removing the mold, the barrier ribs are fired to remove the binder.
European Patent Application EP 0 836 892 A2 describes printing a mixture of a glass or ceramic powder in a binder onto a transfer sheet. The material is printed using a roll or plate intaglio to form barrier rib shapes on the transfer sheet. A substrate is then pressed against the rib material on the transfer sheet to adhere the material to the substrate. After curing the rib material on the substrate, the ribs are fired. The transfer film can be removed before firing or burned away during firing.